Facebook is developing BoltJS, a user interface framework designed to help developers build mobile web apps in HTML5 and JavaScript that run entirely in the browser, with no backend processing required.

BoltJS is built on top of Javelin so that it does not duplicate code already present in the Facebook codebase and so that it is familiar for third-party Facebook developers. The modules are defined using the CommonJS standard, ensuring each module is completely self-contained, with no global variables being created.

BoltJS is written by four individuals right now: Shane O'Sullivan, Will Bailey, Vlad Kolesnikov, and Tom Occhino. O'Sullivan, a software engineer on the Facebook Client UI team, seems to be hosting the project on his personal GitHub account, which has the following project description:

BoltJS is a UI framework designed by Facebook to be compact, fast and powerful. It is written entirely in JavaScript and runs in the browser, needing no server backend. While BoltJS can be used in a progressive enhancement approach, it is primarily designed for UIs that are built mostly, if not completely, in the browser.

While it is the aim of the BoltJS project to support as many modern browsers as sensible, it is currently focused on supporting mobile WebKit browsers, with the intention of being the best possible development platform for mobile sites and HTML5 apps.

While the documentation does reside on GitHub, the source code isn't public yet: the links to the zip and tar source files don't work. Furthermore, there's a BoltJS demo app called Weather App that links to a 404 page. A Google search shows other demo apps, including a few maze games, that lead to dead ends as well.

TechCrunch, which first pointed out BoltJS, believes this has something to do with Project Spartan, Facebook's upcoming HTML5 platform that it may use to challenge Apple, Google, or both in the mobile app space. It's worth noting that the focus of BoltJS (mobile WebKit browsers) is similar to Project Spartan's first target (mobile Safari).

Project Spartan was rumored to be announced in July, but we're already at the end of August now. The latest speculation suggests the project will be officially unveiled later next month, possibly at Facebook's f8 developer conference.